The present invention is directed to bicycles and, more particularly, to a bicycle derailleur with rotation restricting structures.
A bicycle rear derailleur engages a driving chain on one of a plurality of sprockets mounted on the rear wheel hub. A conventional derailleur comprises a base member detachably fastened to the back end the frame, a chain guide for guiding the chain onto the plurality of sprockets, a movable member that pivotably supports the chain guide, and a link mechanism that movably supports the movable member relative to the base member. Such a derailleur is shown in Japanese Unexamined Patent Application No. 11-263282, for example.
Rear dropout portions are formed at the back end of the frame for installing the rear wheel hub and the rear derailleur. The base member may be supported on the frame in a cantilevered manner by screwing a bolt into a threaded opening formed in one of the frame dropout portions. The base member usually is mounted by means of a stopper plate to the rear dropout portion in a manner that allows the base member to pivot relative to the frame. The stopper plate may be mounted on the rear dropout portion in a manner that allows the mounting position of the base member to be adjusted and to restrict the base member from rotating counterclockwise when viewed laterally outwardly from the base member. A coil spring may be disposed between the stopper plate and the base member to bias the base member clockwise and provide tension to the chain.
The chain guide has a pair of vertically aligned pulleys that guide the chain onto one of the plurality of sprockets, wherein the chain guide is pivotably coupled to the moveable member so that the chain guide pivots around an axis that is substantially parallel to the hub axle. The chain guide is biased relative to the movable member in a direction that also produces tension on the chain (typically clockwise when viewed laterally outwardly from the derailleur). The link mechanism may comprise a four-point link mechanism having a pair of links that move the movable member in the direction of the hub axle and diametrically outwardly as the chain guide moves closer to the sprockets. The inner cable of a Bowden cable assembly is fastened to the link mechanism such that pulling or releasing the inner cable using a shifter disposed on the handlebar causes the link mechanism to move the movable member and chain guide to engage the chain with a desired sprocket.
In conventional rear derailleurs, shocks to the bicycle as it runs along rough paths that are extremely uneven, such as those found in mountainous terrain, can sometimes force the base member to pivot counterclockwise against the biasing force of the coil spring. When the base member is thus forced to pivot counterclockwise, the movable member or the chain guide may strike the chain stay of the bicycle frame, thus risking damage to the chain stay, the chain guide or the movable member.